Means for matching the characteristic impedance of a coaxial conductor



M r h 31, 19 A. w. ALFORD MEANS FOR MATCHING THE CHARACTERISTIC IMPEDANCE OF A COAXIAL CONDUCTOR Filed Feb. 13, 1957 INVENTOR.

United States Paten IVIEANS FOR MATCHING THE CHARACTERISTIC IMPEDANCE OF A COAXIAL CONDUCTOR Andrew W. Alford, Winchester, Mass.

Application February 13, 1957, Serial No. 639,870

Claims. (Cl. 333-22) The present invention relates to a means for matching the characteristic impedance of a coaxial conductor. I It is an object of the present invention to provide a means for terminating a coaxial conductor in its characteristic impedance, or, if desired, at some other impedance and, in particular, to provide adjustable means for matching the characteristic impedance of the line to which it is attached.

It is a further object of the present invention to provide means by which almost perfect matches may be obtained.

The structure of the present invention provides a unit which is rugged in nature and is not apt to be accidentally misaligned in handling. It further provides a unit in which adjustments may be made in any desired increment, by varying either the inductance or capacitance.

These and other objects of the present invention will be more clearly understood when considered in connection with the accompanying drawings in which Figure 1 is a top plan view of an embodiment of the invention,

Figure 2 is a cross-sectional elevation taken substantially along the line 2-2 of Figure 1,

Figure 3 is a schematic diagram of the circuitry of Figure 1,

Figure 4 is a fragmentary cross-sectional elevation of a modification of the invention,

Figure 5 is a schematic circuit of the modification shown in Figure 4.

Referring first to the modification illustrated in Figures 1 and 2, there is illustrated a coaxial conductor having inner conductor 1 and outer conductor 2 with the inner and outer conductor suitably spaced by conventional means, such as the dielectric disc 3. At the end of the outer conductor 2 there is formed a peripheral outwardly extending flange 4. The inner conductor 1 is bevelled to a cone shape at end 5. To compensate for the normally high capacitance of this end, the end 5 is bevelled sufficiently to make the capacitance of the end of the conductor too low, in the absence of other compensating means.

Arranged about the flange 4 in symmetrical arrangement are a series of stubs forming conductive stubs 6 and conductive stubs 7. These conductive stubs 6 and 7 should be equal in number. In the illustration shown in Figure 1, six stubs are illustrated. However, six are shown in this modification for illustration purposes only. More or even fewer stubs may be utilized if desired. Each stub is positioned in a radially extending slot cut partially into the upper surface of the flange 4 (as illustrated in Figure 2) whereby these stubs are positioned for longitudinal radial movement toward and away from the inner conductor 1. Each stub is formed with a slot 8 extending longitudinally therethrough. A screw 9 projects through each slot and threads into the flange 4, thus providing means for adjustably securing the stubs at selected positions of longitudinal alignment with the inner conductor 1. The stubs are all tapered at their inner end toward a blunt tip 11.

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The conductive stubs 7 have secured between their blunt tips 11 and the extreme end of the inner conductor 1 the resistors 12. These resistors are interconnected with the stubs 7 and inner conductor 1 by wire sections 13 and 14. These wire sections may be secured at their ends by any suitable means and may be secured as, for example, to the top of the cone section 5 by a screw threaded downwardly into the cone 5, clamping the ends of the wire between the head of the screws and the end of the cone.

Referring now to Figure 3, there is illustrated the schematic circuit equivalent of the structure illustrated,

in Figures 1 and 2 with correspondingly labelled elements. Capacitance'is provided between the blunt tip of the conductive stubs 6 and the inner conductor 1, which capacitance compensates for the low capacitance between the bevelled inner conductor 1 and outer conductor 2. The wire sections 13 and 14 provide inductance in series with the resistor 12 in each of the conductive stubs 7. All these stubs are effectively in parallel with one another and by appropriately adjusting the distance between stubs 6 and inner conductor 1, and between stubs 7 and inner conductor 1, the capacitance and inductance respectively may be eifectively varied. It should be noted, of course, that the Wire sections 1'4 should be sufliciently long as to permit longitudinal adjustment of the stubs 7 while still maintaining the electrical contact along the Wire 14.

While it has been found that the arrangement illustrated in Figure 1 and Figure 2 is satisfactory for obtaining reflector coefiicients below one and one-half percent at frequencies up to 600 megacycles in a 3% inch diameter coaxial line, a modification as illustrated in Figure 4 provides means by which even better matches may be obtained. In this particular modification, improved matching may be obtained over wide frequency band ranges by the expedient of incorporating into the conductive stubs 6 a resistance.

In this arrangement the inner conductor 1 and outer conductor 2, flange 4 and stub 7 are similar to the arrangement previously described. The stub 6 however, is provided with a dielectric sheet 15 covering its inner end. This dielectric sheet 15 faces a conductive plate 16. The conductive plate 16 is freely slideable longitudinally on the surface of dielectric plate 15 and is spaced from the stub 6 by this plate 15. Suitable means, such as a band 17 of dielectric material encircles the stub 6 dielectric plate 15 and plate 16 to provide a guide means permitting free longitudinal sliding movement of the plate 16 with reference to the stub 6 The inner end of the plate 16 is connected to a resistor 18, in turn connected to the tip of the cone 5 by the wire 19.

The arrangement as shown in Figure 4 finds its equivalent schematic circuit in Figure 5. This schematic circuit is similar to that illustrated in Figure 3 with the exception that there is now provided in series with the capacitance formed by stub 6 a resistor 18. The magnitude of the components, as for example the resistance utilized in both modifications, should be selected by known means.

In the arrangement of Figure 3 the capacitance in series with stubs 6 are adjusted so as to make the termination a pure resistance in spite of inductances in series with the resistors.

In the arrangement of Figures 4 and 5, the input impedance of the termination shown in Figure 5 would be a pure resistance. When resistors 18 in series with the capacitances were equal to resistors 12 in series with the inductances and the relations between the inductances and capacitances and the resistors were given by R =L/C in which R is the resistance of one of the resistors, L is the inductance in series with one of the a .stubs and C is the capacitance in series with one of the other stubs. When the individual inductances, capacitances and resistors are not quite equal to each other, the. relation R =L/ C still holds except that in this case the R, L and C refer to approximately the average value of these circuit parameters.

Having now described my invention, I claim:

1. In combination with a coaxial line having inner and outer conductors, means for adjustably matching and where desired compensating for the characteristic impedance thereof comprising a plurality of stubs radially arranged about said inner conductor and disposed between the inner and outer conductors, means adjustably securing said stubs to said outer conductor for adjustments toward and away from said inner conductor whereby the effective dielectric spacing between said inner and outer conductors may be effectively adjusted, series resistive and inductive means interconnecting alternate stubs with said inner conductor whereby inductive compensating elements are provided, said other stubs providing capacitive compensating elements.

2. In combination with a coaxial line having inner and outer conductors, means for adjustably matching and Where desired compensating for the characteristic impedance thereof, comprising a plurality of radially arranged variable inductive and capacitive compensating elements disposed between the inner and outer conductors, said inductive elements including series resistance and inductance means interconnecting said inner and outer conductors, said capacitive elements intercoupling said inner and outer conductors, and means for eflectiv'ely adjusting the magnitude of the inductance and capacitance of said elements by varying the radial location thereof.

3. In combination with a coaxial line having inner and outer conductors, means for adjustably matching and where desired compensating for the characteristic impedance thereof, comprising a plurality of radially arranged variable inductive and capacitive compensating elements, said inductive elements each comprising an inwardly extending stub adjustably secured to said outer conductor with a series resistance and inductance extending therefrom to said inner conductor, said capacitive elements each comprising an inwardly extending stub adjustably secured to said outer conductor, and means adjustably securing said stubs to said outer conductor adapted to permit adjustment toward and away from said inner conductor whereby the effective inductance and capacitance of said elements may be varied.

4. In combination with a coaxial line having inner and outer conductors with a peripheral end flange extending outwardly from said outer conductor, means for matching and where desired compensating for the characteristic impedance of said coaxial conductor comprising a plurality of conductive stubs radially arranged about said inner conductor and disposed between the inner and outer conductors, means adjustably securing said stubs to said flange for radial movement toward and away from said inner conductor, means forming a series inductance and resistance between each of a portion of said stubs and said inner conductor, said inductances being adjustable in response to movement of said portion of said stubs and said other stubs forming capacitive compensating means.

5. In combination with a coaxial line having inner and outer conductors with a peripheral end flange extending outwardly from said outer conductor, means for matching and where desired compensating for the characteristic impedance of said coaxial conductor comprising a plurality of conductive stubs radially arranged about said inner conductor and disposed between the inner and outer conductors, means adjustably securing said stubs to said flange for radial movement toward and away from said inner conductor, inductive series connections each of a resistor and wire extending from either end thereof connected rigidly at one end and slideably at the other end between each of a portion of said stubs and said inner conductor and said other stubs each forming capacitive compensating means.

6. A device as set forth in claim 5 wherein said series connections and said other stubs are equal in number.

7. A device as set forth in claim 4 wherein said securing'means comprise means forming longitudinally extending slots in each stub and clamping screws extending through said slots into said flange.

8. A device as set forth in claim 5 wherein said other stubs are each formed with resistance in series therewith.

9. In combination with a coaxial line having inner and outer conductors, means for adjustably matching and where desired compensating for the characteristic impedance thereof, comprising, a plurality of radially arranged variable inductive and capacitive compensating elements disposed between the inner and outer conductors, said inductive elements including series resistance and inductance means interconnecting said inner and outer conductors, said capacitive elements intercoupling said inner and outer conductors, and means for elfectively adjusting the magnitude of the inductance and capacitance of said elements.

10. A combination in accordance with claim 9 and further comprising respective resistance elements in series with said capacitive elements.

No references cited. 

